Add STSAFE-A120 Support #9614

dgarske · 2026-01-06T00:38:14Z

Add STSAFE-A120 Support via STSELib

Description

This PR adds support for the ST STSAFE-A120 secure element using the open-source STSELib SDK. The STSAFE-A120 is ST's latest secure element with enhanced cryptographic capabilities and is the successor to the STSAFE-A100/A110 series.

Changes

Files Modified:

wolfcrypt/src/port/st/stsafe.c - Added STSAFE-A120/STSELib implementation
wolfssl/wolfcrypt/port/st/stsafe.h - Added type abstractions and curve mappings
wolfcrypt/src/wc_port.c - Updated STSAFE initialization
wolfcrypt/src/port/st/README.md - Added documentation

Features

True Random Number Generation (TRNG) - Hardware RNG for seeding wolfSSL's RNG
ECC Key Generation - P-256 and P-384 key pair generation in secure element
ECDSA Sign/Verify - Hardware-accelerated ECDSA operations
ECDH Shared Secret - Elliptic curve Diffie-Hellman key exchange
Device Certificate - Read X.509 certificates from secure storage
Crypto Callbacks - Full integration with wolfSSL's crypto callback mechanism

Configuration

Enable with:

#define WOLFSSL_STSAFEA120Optional defines:
#define USE_STSAFE_RNG_SEED    /* Use STSAFE for RNG seeding */
#define WOLF_CRYPTO_CB         /* Enable crypto callbacks */
#define STSAFE_I2C_BUS 1       /* I2C bus number (default: 1) */

Dependencies

STSELib - ST Secure Element Library (BSD-3-Clause)
- Available from: https://github.com/STMicroelectronics/STSELib
- Requires platform abstraction layer implementation

API Compatibility

The new implementation maintains API compatibility with the existing STSAFE-A100 code:

stsafe_interface_init() - Initialize device
wolfSSL_STSAFE_CryptoDevCb() - Crypto callback handler
SSL_STSAFE_* callback functions for TLS integration

Testing

Tested on Raspberry Pi 5 with STSAFE-A120 connected via I2C:

Echo command ✅
Random number generation ✅
ECC P-256 key generation ✅
ECC P-384 key generation ✅
ECDSA P-256 sign/verify ✅
ECDSA P-384 sign/verify ✅
Crypto callback integration ✅

Performance (Raspberry Pi 5)

Operation	Time
ECC P-256 KeyGen	~40 ms
ECDSA P-256 Sign	~51 ms
ECDSA P-256 Verify	~79 ms
RNG (256 bytes)	<1 ms

Notes

The STSELib uses conditional compilation for ECC curves via stse_conf.h
Curve ID values in stsafe.h depend on which curves are enabled in stse_conf.h
Default configuration enables NIST P-256 and P-384

check-all-return-codes snippet: Capture the return value of stsafe_interface_init() in wolfCrypt_Init and, if it is non-zero, propagate or handle the error (e.g., ret = stsafe_interface_init(); if (ret != 0) return ret;).
no-memory-leaks snippet: After copying the shared secret, add XFREE(sharedSecret, NULL, DYNAMIC_TYPE_TMP_BUFFER); (and similarly free other SDK-allocated buffers such as pubX/pubY, signature, readBuf, echo_resp) before the function returns.
limit-stack-usage snippet: Replace large local buffers (e.g., sigRS, pubKeyX, pubKeyY in SSL_STSAFE_VerifyPeerCertCb) with heap allocations under the WOLFSSL_SMALL_STACK pattern, freeing them before return.

@dgarske
please take a look at the above issues which Devin flagged. Devin will not fix these issues automatically.

dgarske · 2026-01-07T00:02:26Z

Jenkins retest this please: "AgentOfflineException"

JacobBarthelmeh · 2026-01-09T18:49:55Z

wolfcrypt/src/port/st/stsafe.c

+        0, 0, 4, &readBuf, STSAFE_A_NO_MAC);
+
+    if (status_code == STSAFE_A_OK && readBuf->Length == 4 &&
+        readBuf->Data[0] == 0x30) {


Instead of 0x30, 0x81, and 0x82 use ASN_SEQUENCE | ASN_CONSTRUCTED and the ASN length values. If this is hard set to avoid needed NO_ASN not defined then please add comments as to what the values are here.

JacobBarthelmeh · 2026-01-09T18:51:53Z

wolfcrypt/src/port/st/stsafe.c

+    }
+
+    if (rc == STSAFE_A_OK && *pCertLen > 0) {
+        step = 223 - (stsafe_a->CrcSupport ? 2 : 0);


Magic number here of 223.

JacobBarthelmeh · 2026-01-09T19:02:05Z

wolfcrypt/src/port/st/stsafe.c

+        r_length = ((uint16_t)signature->Data[0] << 8) | signature->Data[1];
+        s_length = ((uint16_t)signature->Data[2 + r_length] << 8) |
+                   signature->Data[3 + r_length];
+


There should be bounds checks here on r_length and s_length before use. It's unlikely that the ST function will return invalid or unexpected data with a status_code return of STSAFE_A_OK but better to have a sanity check.

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dgarske · 2026-01-12T22:18:43Z

Jenkins retest this please: "AgentOfflineException"

Copilot

Pull request overview

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Copilot · 2026-01-15T20:12:10Z

wolfcrypt/src/port/st/stsafe.c

+
+                        ret = stse_generate_ecc_key_pair(&g_stse_handler, slot,
+                            (stse_ecc_key_type_t)curve_id,
+                            STSAFEA_EPHEMERAL_KEY_USAGE_LIMIT,


The macro STSAFEA_EPHEMERAL_KEY_USAGE_LIMIT is used but never defined anywhere in the codebase. This will cause a compilation error. This should likely be a numeric literal (e.g., 255) or defined as a macro in the header file.

Copilot · 2026-01-15T20:12:11Z

wolfcrypt/src/port/st/stsafe.c

+                    if (need_ephemeral_key) {
+                        /* Key is in slot 1 (for ECDSA), but ECDH requires ephemeral slot.
+                         * Generate ephemeral key pair for ECDH. Note: This will overwrite any
+                         * existing key in ephemeral slot, so for bidirectional ECDH, both keys
+                         * should be generated in ephemeral slot from the start. */
+                        stse_ReturnCode_t ret;
+                        byte ephemeralPubKey[STSAFE_MAX_PUBKEY_RAW_LEN];
+                        int key_sz = stsafe_get_key_size(curve_id);
+                        slot = STSAFE_KEY_SLOT_EPHEMERAL;
+
+                        ret = stse_generate_ecc_key_pair(&g_stse_handler, slot,
+                            (stse_ecc_key_type_t)curve_id,
+                            STSAFEA_EPHEMERAL_KEY_USAGE_LIMIT,
+                            ephemeralPubKey);


This code block uses A120-specific types (stse_ReturnCode_t) and functions (stse_generate_ecc_key_pair) without #ifdef WOLFSSL_STSAFEA120 guards. This will cause compilation errors when building with WOLFSSL_STSAFEA100 defined. The entire block from lines 1854-1892 should be wrapped in #ifdef WOLFSSL_STSAFEA120 ... #else ... #endif to provide appropriate implementation for both A100 and A120.

Copilot · 2026-01-15T20:12:11Z

wolfcrypt/src/port/st/stsafe.c

+#ifdef WOLFSSL_STSAFEA120
+                stse_ReturnCode_t ret;
+                slot = STSAFE_KEY_SLOT_1;  /* Use persistent slot for ECDSA signing */
+                ret = stse_generate_ecc_key_pair(&g_stse_handler, slot,
+                    (stse_ecc_key_type_t)curve_id,
+                    255,  /* usage_limit for persistent keys */
+                    pubKeyRaw);


The magic number 255 for usage_limit should be defined as a named constant (e.g., STSAFE_PERSISTENT_KEY_USAGE_LIMIT) for better code maintainability and consistency. This same value should be used throughout the codebase where applicable.

Copilot · 2026-01-15T20:12:11Z

wolfcrypt/src/port/st/stsafe.c

+                        byte ephemeralPubKey[STSAFE_MAX_PUBKEY_RAW_LEN];
+                        int key_sz = stsafe_get_key_size(curve_id);


The variable key_sz is declared but only used within the STSAFE-A120 specific code path at line 1881. This variable declaration should be moved inside the A120-specific #ifdef block (after adding the missing guards) to avoid unused variable warnings.

Suggested change

byte ephemeralPubKey[STSAFE_MAX_PUBKEY_RAW_LEN];

int key_sz = stsafe_get_key_size(curve_id);

byte ephemeralPubKey[STSAFE_MAX_PUBKEY_RAW_LEN];

#ifdef WOLFSSL_STSAFEA120

int key_sz = stsafe_get_key_size(curve_id);

#endif

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dgarske self-assigned this Jan 6, 2026

dgarske mentioned this pull request Jan 6, 2026

[platform/wolfssl] Add wolfCrypt crypto platform support STMicroelectronics/STSELib#54

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dgarske force-pushed the stsafe-a120 branch from 7a8e71b to 2e8c1da Compare January 6, 2026 22:56

dgarske assigned wolfSSL-Bot and unassigned dgarske Jan 8, 2026

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dgarske added 3 commits January 12, 2026 11:32

Add STSAFE-A120 Support

297f4a3

Cleanup WOLFSL_STSAFE and fix issue with multi-test macros

a5a19c1

Fixes for peer review.

59e6db9

dgarske force-pushed the stsafe-a120 branch from 2e8c1da to 59e6db9 Compare January 12, 2026 20:36

Added ECDHE support

ed82b91

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Peer review cleanups. ECDHE improvements.

1dde828

dgarske requested a review from Copilot January 16, 2026 00:18

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		byte ephemeralPubKey[STSAFE_MAX_PUBKEY_RAW_LEN];
		int key_sz = stsafe_get_key_size(curve_id);

Add STSAFE-A120 Support #9614

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dgarske commented Jan 6, 2026 • edited Loading Uh oh! There was an error while loading. Please reload this page.

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Add STSAFE-A120 Support via STSELib

Description

Changes

Features

Configuration

Dependencies

API Compatibility

Testing

Performance (Raspberry Pi 5)

Notes

Related

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dgarske commented Jan 6, 2026 •

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